<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            width: 200px;
            height: 200px;

            /* 控制文本的水平居中 */
            text-align: center;
            /* 控制文本的垂直居中 */
            line-height: 200px;

            background-color: aqua;
        }
    </style>
</head>

<body>
    <div class="box">
        hello
    </div>
</body>

</html>